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Astronomy 1010: The Solar System

Astronomy 1010: The Solar System. Prof. Paul J. Wiita Rm 715, One Park Place, wiita@chara.gsu.edu Phones: 404-413-6022 (office); 609-273-7177 (cell) URL: www.chara.gsu.edu/~wiita (syllabus, summaries of notes)

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Astronomy 1010: The Solar System

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  1. Astronomy 1010: The Solar System • Prof. Paul J. Wiita • Rm 715, One Park Place, wiita@chara.gsu.edu • Phones: 404-413-6022 (office); 609-273-7177 (cell) • URL: www.chara.gsu.edu/~wiita (syllabus, summaries of notes) • Assignments on Mastering Astronomy: www.masteringastronomy.com with course ID MAWIITA1010S10 • Labs: in 528 Kell Hall • 10144: Tuesdays, 1:00-2:50 PM • 10145: Wednesdays, 2:30-4:20 PM • 10142: Fridays, 9:00-10:50 AM

  2. What will we study? • Astronomy = star + knowledge • We examine night sky and planets.

  3. The Scientific Method We will frequently refer to the concepts of the Scientific Method, and even when we don’t, you should be thinking about how it applies in each part of the course (and throughout your life!). The key element is curiosity! I hope your previous studies haven’t completely eliminated that characteristic from your personality. How do we learn anything about the Universe?

  4. The First Steps in the Scientific Method • Observe: use your senses or augmentations of them (microscope or telescope). Example: the sky is blue. • Hypothesize (come up with a possible explanation of the observation). Someone has painted it blue. The blue color is a reflection of the oceans. Blue light is more easily scattered than red in the atmosphere, so the blue sky is scattered sunlight. 3. Test HYPOTHESIS through a PREDICTION. If the latter is true, then if sunlight passes through more of the atmosphere, the sun should lose green and yellow light too and appear red. (When does this happen?)

  5. Blue light scatters more in the atmosphere • Off molecules (strongly) and off dust (less so, however).

  6. Testing Hypotheses 4a. perform EXPERIMENT 4b. OR make new OBSERVATIONSun is indeed red/orange near dawn and dusk 5a. If in agreement, perform new test (and keep doing so). 5b. If in disagreement, discard or modify hypothesis GO BACK TO STEP 2! Only if MANY tests are passed can a HYPOTHESIS be called a THEORY. If the THEORY applies in a wide range of situations, it may be raised to the status of a LAW (e.g., Newton's LAW of Gravity)

  7. In SCIENCE nothing is ever PROVEN STILL, even a LAW can be wrong (or partly right): Einstein showed that Newton's Laws don't hold exactly if: • velocities are close to the speed of light (special relativity) OR if • lots of mass is concentrated in a small volume (general relativity). SO NOTHING IN A REAL SCIENCE IS EVER ABSOLUTELY PROVEN TRUE, although most of what is discovered and tested in a "hard" science is VERY LIKELY to be correct.

  8. Types of “Hard” Sciences • Categorize: astronomy, biology, chemistry, geology, medicine, meteorology, oceanography, physics as • OBSERVATIONAL or EXPERIMENTAL sciences.

  9. The REAL Scientific Method • But the preceding is idealized. • In reality, even good scientists often don't discard hypotheses when they fail an experimental or observational test. • Why not? • A. Experiment is wrong. • B. Experiment is misinterpreted. • C. Psychological/sociological/political difficulty in giving up long-held beliefs. • Eventually the weight of evidence becomes overwhelming and there is a PARADIGM SHIFT or SCIENTIFIC REVOLUTION.(e.g., Copernican, Darwinian, Quantum Mechanics)

  10. Characteristics of Sciences • The above are characteristics of ANY SCIENCE. • The key point: scientific results are falsifiable. • If they cannot eventually be tested, they fall outside the realm of science and enter philosophy, religion, etc. • Pseudo-sciences do not allow themselves to be tested and “true believers” refuse to consider strong evidence against their validity. Examples: ? • astrology, alchemy, numerology, palmistry, crystal/pyramid power

  11. What A Science Must Have

  12. Types of Sciences • What about: anthropology, economics, history, political science, psychology, sociology? • These social or "soft" sciences rely to one extent or another on scientific methods, but also invariably carry a great number of preconceptions that allow for many disparate interpretations to be drawn from the same data. Usually too many complications. • In the natural or "hard" sciences, the range of “allowed” interpretations is usually much less and new experiments or observations can be designed to choose the best.

  13. Astronomy vs. Astrophysics • Aside from the OBSERVATIONAL - EXPERIMENTAL dichotomy, since the advent of calculus we have distinguished these approaches from THEORETICAL science, driven by applied mathematics. • ASTRONOMY IS AN OBSERVATIONAL SCIENCE. • ASTROPHYSICS IS AN OBSERVATIONAL -THEORETICAL - EXPERIMENTAL SCIENCE. • Today we typically use these terms interchangeably since so much of what we learn combines observations with theory and some experimental work (laboratory astrophysics). • We also must consider COMPUTATIONAL science as a (nearly) equal partner now that computers are so powerful.

  14. Review of Scientific Notation • 102 = 100, 101=10, 100 = 1, 10-1=0.1, 10-2=0.01 • 1012=1,000,000,000,000=trillion (Tera-) • 109 =1,000,000,000 = billion (Giga-) • 106 = 1,000,000 = million (Mega-) • 103 = 1,000 = thousand (kilo-) • 10-2= 0.01=one-hundredth (centi-) • 10-3= 0.001=one-thousandth (milli-) • 10-6= 0.000001=one-millionth (micro-) • 10-9= 0.000000001=one-billionth (nano-) • 5.4x103=5,400 7.05x10-3=0.00705 • 4,700=4.7x103 0.017 = 1.7x10-2

  15. Powers of Ten Arithmetic Multiplication: (5.3x103) x (6x10-5) = 31.8x103+(-5) =31.8x10-2 = 3.18x10-1 =0.318 = 0.3 One significant figure! Keep only the minimum number of significant figures going into the calculation in the answer. Division: (9.3 x10-4)/(3.10x10-6) = 3.0 x10-4-(-6) = 3.0 x102 = 300 BUT, 3.0x102 is the better answer, as it CLEARLY has two significant figures; scientific notation is PRECISE.

  16. The Scales of the Universe We deal with the largest possible things -- the whole universe -- and with the smallest -- nuclei of atoms. This requires us to use a wide range of PHYSICAL UNITS and we USE THE METRIC SYSTEM. Length: m or cm Mass: kg or g Time: s or yr Temperature: K(elvins) 1 pc = 3.26 light-yr = 3.085678 x 1018cm=3.1x1013km 1AU = 1.496x1013cm = 150,000,000 km (astronomical unit = mean distance between earth and sun)

  17. Sizes of Everything • Universe: open or flat -- infinite; closed -- 1028cm • Galaxies: no of stars 109-1013; size ~ 1023cm~3x104pc • Stars: 1010-1012cm (most radii) • Typical separations: 1018cm ~ 1 pc • Planets: RE=6.4x103km = 6.4x108cm • Separations: ~ 1 AU • Mountain: Tallest ~ 10 km, more typical ~6 km Hm/RE=6.4km/6.4x103km=1.0x10-3 • People: 1.5m = 1.5x102cm (~5 feet) • Visible light: wavelength=500nm=5x10-5cm • Atom: 0.1nm=10-8cm=10-10m (X-ray wavelength) • Nucleus: 1 Fermi = 10-13cm = 10-15m • Zoom from the Universe to You

  18. Time Scales of the Universe • Time since the Big Bang: ~1.4x1010 yr • Galaxies formed: ~1.3x1010 yr ago • Solar system formed: 4.55x109 yr ago • Oldest rocks on Earth: 3.8x109 yr BP • Earliest life forms: ~3.5x109 yr BP • Earliest hominids:~2x106 yr BP • Mountains: Appalachians:~2.5x108yr BP; Rockies: 7x107 yr BP • Human lifespan: ~75 yr • Oscillation time for visible light: ~2x10-15 s • Time for light to pass the nucleus of an atom: ~3x10-24s

  19. Astronomy 1010 Lab RequirementsBring to lab next week • Activities in Astronomy: by John W. Wilson • Metric ruler ~ 30 cm long • Protractor • Drawing compass • Scientific calculator (not a cell phone)

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